AC Coupled Multistage Amplifiers The output of one amplifier is the input to the next amplifier. The overall gain: where or Note the DC bias circuits are isolated from each other by the coupling capacitors. The DC calculations are independent of the cascading. The AC calculations for gain and impedance are interdependent. 1   k k i L Z Z 1   k k o s Z Z n k v v v v v A A A A A       2 1